I. Field of the Invention
The present invention relates to communications systems. More particularly, the present invention relates to a novel and improved method for encrypting data for security in wireless communication systems.
II. Description of the Related Art
In a wireless communication system, it is desirable for the service provider to be able to verify that a request for service from a remote station is from a valid user. In some current cellular telephone systems, such as those deploying the AMPS analog technology, no provision is made to deter unauthorized access to the system. Consequently, fraud is rampant in these systems. One fraudulent means for obtaining service is known as cloning, in which an unauthorized user intercepts the information necessary to initiate a call. Subsequently, the unauthorized user can program a mobile telephone using the intercepted information and use that telephone to fraudulently receive telephone service.
To overcome these and other difficulties, many cellular telephone systems have implemented authentication schemes such as that standardized by the Telecommunications Industry Association (TIA) in EIA/TIA/IS-54-B. One facet of this authentication scheme is encryption of information, transmitted over the air, that is required to receive service. This information is encrypted using the Cellular Message Encryption Algorithm (CMEA). The CMEA algorithm is disclosed in U.S. Pat. No. 5,159,634, entitled "CRYPTOSYSTEM FOR CELLULAR TELEPHONY", incorporated by reference herein.
Several major weaknesses have been discovered in CMEA which allow encrypted information to be deciphered using current standard computational equipment in a relatively short period of time. These weaknesses will be thoroughly outlined hereinafter followed by a description of the present invention which overcomes these weaknesses. CMEA has been published on the Internet, hence these weaknesses are open for discovery by anyone with an interest in doing so. Thus, a new algorithm for encryption is desirable to replace CMEA to avoid the interception and fraudulent use of authentication information necessary to initiate cellular service.